The invention relates to a directionally adjustable telescope arrangement having a first arcuate mirror, a second arcuate mirror and a planar deflection mirror.
A directionally adjustable telescope arrangement of the above kind is especially suitable for a stabilized aerial image camera or a reconnaissance camera.
Such a directionally adjustable telescope arrangement is disclosed in European patent publication 0,385,079. This telescope arrangement is provided for use in a track vehicle and is a mirror telescope according to Cassegrain having a Nasmyth arrangement wherein a central bore of the main mirror is avoided in that a planar mirror deflects the beam by 90xc2x0 forward of the main mirror, that is, before a first arcuate mirror.
In this known telescope arrangement, the second arcuate mirror is configured as a convex mirror and, to change the field of view, the second arcuate mirror can be exchanged for another convex mirror. In this way,. this telescope arrangement, which only has two imaging-effective arcuate mirrors, has either a field of view of 1xc2x0 or a field of view of 3xc2x0.
It is an object of the invention to provide an improved directionally adjustable telescope arrangement having a high light intensity and a large field of view.
The directionally adjustable telescope arrangement of the invention includes: a first arcuate mirror for receiving an incoming beam traveling along a sight line of the telescope arrangement and for deflecting the beam along an imaging beam path; a second arcuate mirror arranged in the imaging beam path for receiving and deflecting the beam and the imaging beam path; a planar deflecting mirror for receiving and deflecting the beam and imaging beam path deflected from the second arcuate mirror; a third arcuate mirror arranged in the imaging beam path; and, the first, second and third arcuate mirrors conjointly effecting an imaging of the beam along the imaging beam path.
With the three optically-effective arcuate mirrors, a large light intensity and a large field of view (for example, up to 15xc2x0 field of view diameter) are possible with an improved correctibility of the imaging errors.
Especially directionally adjustable telescope arrangements having a large field of view and/or a high light intensity basically require a large input pupil and this requires a high primary aperture ratio of the main mirror (that is, the first arcuate mirror) and considerable readjustment of magnification via the additional optically active elements. For these reasons, an optimal correctibility of the imaging errors by means of the at least three aspherically configurable surfaces is of great significance.
In an advantageous embodiment of the invention, the first arcuate mirror and the second arcuate mirror are mounted inclined relative to the viewing direction of the telescope arrangement and the second arcuate mirror lies outside of the beam path extending from the input end to the first arcuate mirror. In this way, shading by the second arcuate mirror and, possibly, the planar deflecting mirror, which is considerable especially for light intense Cassegrain telescope arrangements, can be avoided. The shading reduces the light intensity as well as the imaging quality. Furthermore, the planar deflecting mirror can in this way be so mounted that it is no longer surrounded by the imaging beam whereby, for a motorized rotatable deflecting mirror, the design requirements as to the drive are considerably reduced and this has very positive effects on the sensitivity and the accuracy of the drive and thereby also on the imaging quality.
In the event that the telescope arrangement has a detector housing and a viewing head, which is pivotable about a directional axis and accommodates the first arcuate mirror and the second arcuate mirror, then the directional adjustment range of the telescope arrangement can be especially great. For a viewing head, which is configured as a rotatable sphere having its own window, a directional adjustment range of plus/minus 140xc2x0 referred to a longitudinal axis of the telescope arrangement can be achieved which, in the case of an aerial image camera, would correspond to the direction of flight. However, even for a viewing window which is mounted fixedly to the detector housing, a large directional angle is obtained with this embodiment.